I'm an immunologist and I'll defend immunology to my- to my last breath, but it is true that if the successes in AIDS control in Africa have been through education and spreading the use of protection rather than- physical barriers, condoms- rather than through immunology, and that turns out on a mass scale to be actually a lot cheaper than vaccination, so well, I think it's obvious that there are- that at any one time there are plenty of options. Some options are better than others, more likely to work than others, but we should push on with- with whatever we can. In the field of tuberculosis research, which is a bigger killer than HIV, it's probably true that at this moment there's vastly more to be done with the development of new antibiotics and their application and their testing than ever there is with immunology. It does not mean we should give up on trying to build an anti-microbacterial vaccine, set of vaccines.

Avrion Mitchison, the British zoologist, is currently Professor Emeritus at University College London and is best known for his work demonstrating the role of lymphocytes in tumour rejection and for the separate and cooperative roles of T- and B-lymphocytes in this and other processes.

Martin Raff is a Canadian-born neurologist and research biologist who has made important contributions to immunology and cell development. He has a special interest in apoptosis, the phenomenon of cell death.